An organic electroluminescence element (hereinafter, also referred to as an organic EL element) includes a pair of electrodes and a thin film containing an organic electroluminescence material (hereinafter, also referred to as an “organic EL material”) located between the pair of electrodes. Such an organic EL element emits light as follows. A singlet exciton, generated by recombination of a hole and an electron caused by a host molecule in the light emitting layer, causes energy transfer to a fluorescent molecule, which is a light emitting dopant. As a result, the fluorescent molecule emits light. The intensity of light emission of the organic EL element is controllable by the level of voltage to be applied or by the amount of electric current flowing in the element. A display device including a display screen that includes pixels formed by use of this characteristic has been developed.
A display device using an organic EL element is capable of displaying an image by controlling light emission of individual pixels independently. Therefore, the display device does not require a backlight unit, which is required in a transmission-type liquid crystal display device, and thus is made thinner. In such an organic EL display device, a host material is doped with a light emitting dopant to form a light emitting layer. Therefore, a technology has been reported by which the amount of the light emitting material used for the doping is set to be maximized at a peak emission position at which the density of holes and electron is highest in a thickness direction of the light emitting layer, from the point of view of improving the light emission efficiency of, and extending the life of, the organic EL display device (Japanese Laid-Open Patent Publication No. 2007-201198).
Japanese Patent No. 4649676 describes that a region doped with a dopant providing an electron injection characteristic and/or an electron transfer characteristic includes, arranged in a thickness direction, an organic dopant region doped with an organic dopant and a metal dopant region doped with a metal dopant, and that the organic dopant region is located between a light emitting region doped with a dopant providing a light emitting characteristic and the metal dopant region. Japanese Patent No. 4649676 also describes that the light emitting region partially overlaps at least one of a hole dopant region and an electron dopant region in the thickness direction. Japanese Laid-Open Patent Publication No. 2010-226055 describes an EL organic display device including a first organic EL element including an organic layer, containing a first dopant material, between a pixel electrode and a counter electrode; and a second organic EL element including an organic layer, extending from the first organic EL element, between the pixel electrode and the counter electrode, the organic layer containing a second dopant material that is an isomer of the first dopant material.